The present invention relates to a shift control system for an automatic transmission capable of effecting an automatic shifting and a manual shifting and having a plurality of kinds of engage/release combinations of frictional engagement members for achieving a predetermined one of gear stages.
As is well known in the art, the automatic transmission for vehicles is required not only to be smallsized and lightweight and excellent and excellent in durability but also to be easily controlled for a shifting and have less shift shocks. Generally in the prior art, therefore, the controls for the shifting are facilitated, and the shift shocks are reduced by using a one-way clutch as engagement means for connecting or holding the rotating members of a gear train to change the engage/release states of the rotating members in accordance with the direction of torque application.
In dependence upon the structure of the gear train, however, the one-way clutch cannot be applied at all times to execute the shifting, but the shifting is sometimes executed by timing two frictional engagement means such as a multi-disc clutch and a multidisc brake or a band brake in their engagements or releases. In an automatic transmission capable of having a plurality of engage/release combinations (or patterns) of the frictional engagement means for one gear stage, on the other hand, the shifting for applying the one-way clutch is sometimes increased as much as possible by changing the engage/release patterns with that gear stage being set.
In the automatic transmission having a plurality of kinds of engage/release patterns for setting one gear stage, the aforementioned controls for changing the engage/release patterns can be accomplished to reduce the shift shocks. Since, moreover, any of the rotating members may have its rotational speed increased or decreased in accordance with some engage/release pattern, this engage/release pattern can be changed over to suppress the fluctuations in the rotational speed accompanying the shifting to reduce the shift shocks or to improve the durability of the frictional engagement means.
In the automatic transmission capable of selecting the plural engage/release patterns for each gear stage, the change-over of the engage/release patterns is effective at a predetermined gear stage so as to satisfy the aforementioned various requirements. In this case, the time period required for executing the shifting is naturally elongated.
Incidentally, a shifting in the automatic transmission is automatically effected by engaging or releasing the frictional engagement means on the basis of the running conditions such as the throttle opening or the vehicle speed. This change-over of the engage/release of the frictional engagement means can be caused in response to an (electric or hydraulic) output signal generated by the manual operation. The automatic transmission, if equipped with such mechanism, can perform both the automatic shifting and the manual shifting.
In the automatic transmission of this kind capable of interchanging the automatic-manual shifts, too, the several engage/release patterns, if any, of the frictional engagement means for establishing a predetermined gear stage are effectively switched at the gear stage to make the shifting possible by using a one-way clutch, for example, and to suppress the fluctuations in the rotational speeds of the rotating members. In case of the manual shift mode for the driver to time the shifting sensually, however, the time period for the shifting is elongated to cause a disadvantage in the apparently inferior responsiveness to the shifting, if a shift control is performed through another gear stage as in the automatic shift mode so as to avoid the simultaneous shifting.